Soaring birds

To: Birding-Aus <>
Subject: Soaring birds
From: John Anselmi <>
Date: Wed, 11 Jun 1997 14:17:00 -0700
I am a glider pilot and consequently have great admiration of bird flight, and 
particular, soaring flight.

It is the energy aspects of soaring flight which intrigue me most.  While I 
have no 
measurements to support my ideas, it seems that soaring birds use very little 
diring soaring flight.  It may be cosidered that, compared with flapped flight, 
soaring flight saves energy roughly in the ratio of the bird's glide ratio ie 
12:1.  Even this does not seem to quite fit in with the time soaring birds 
spend in 
what appears to be flight for flight's sake.  Recently we were on Mt Gower on 
Howe Island and saw the Providence Petrels spending what appeared to be most of 
day soaring over the saddle between the two mountains.  Likewise I have met 
wedge-tailed eagles at over 9,000 feet.  They may have been marking their 
or they may have been there to get cool - it was on hot days - but in either 
case it 
would take a considerable amount of energy if there are no energy saving 
features in 
the eagle's physiology.

It would seem to me that if soaring birds have to hang on their pectoral 
muscles they 
would not have such a great saving over flapping birds unless there were 
physiological differences.  These differences may be:

1)      some means of locking their "shoulders" so that the weight was not 
carried on 
the pectoral muscles (cf. our knees, horses rear legs etc);

2)      the pectoral muscles fully extended when in soaring position so that 
was not needed to maintain that position;

3)      different muscle type in the pectoral muscles adapted for continuous 
load in 
soaring birds;

4)      some other way of breathing - I understand the act of flapping moves 
air in 
and out of the bird's lungs;

5)      some other way of moving blood through the pectoral muscle tissue - 
birds would not have the flapped flight expansion/contraction cycles which move 

The other line of reasoning is that in nature, if an efficiency can be made, it 
usually found somewhere.  Therefore I would expect some soaring birds to show 
specialisation which maximises the efficiency of soaring flight.

I would be most interested to receive any suggestions which may satisfy my 

John Anselmi

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